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J. Biol. Chem., Vol. 282, Issue 19, 14373-14378, May 11, 2007

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MukE and MukF Form Two Distinct High Affinity Complexes^*

Melanie Gloyd¹, Rodolfo Ghirlando¹, Lindsay A. Matthews², and Alba Guarné³

From the Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8N 3Z5, Canada and the Laboratory of Molecular Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0540

The MukBFE complex is essential for chromosome segregation and condensation in Escherichia coli. MukB is functionally related to the structural maintenance of chromosomes (SMC) proteins. Similar to SMCs, MukB requires accessory proteins (MukE and MukF) to form a functional complex for DNA segregation. MukF is a member of the kleisin family, which includes proteins that commonly mediate the interaction between SMCs and other accessory proteins, suggesting that the similarities between the MukBFE and the SMC complexes extend beyond MukB. Although SMCs have been carefully studied, little is known about the roles of their accessory components. In the present work, we characterize the oligomeric states of MukE and MukF using size exclusion chromatography and analytical ultracentrifugation. MukE self-associates to form dimers (K_D 18 ± 3 µM), which in turn interact with the MukF dimer to form two distinct high affinity complexes having 2:2 and 2:4 stoichiometries (F:E). Intermediate complexes are not found, and thus we propose that the equilibrium between these two complexes determines the formation of a functional MukBFE with stoichiometry 2:2:2.

Received for publication, February 16, 2007

^* This work was supported by Canadian Institutes of Health Research (MOP 67189) and in part by the Intramural Research Program of the NIDDK, National Institutes of Health (to R. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1-S3.

¹ Both authors contributed equally to this work.

² Supported by an undergraduate student research award from the National Sciences and Engineering Research Council of Canada.

³ To whom correspondence should be addressed: Dept. of Biochemistry and Biomedical Sciences, HSC-4N57A, McMaster University, 1200 Main St. West, Hamilton, ON L8N 3Z5, Canada. Tel.: 905-525-9140 (ext. 26394); Fax: 905-522-9033; E-mail: guarnea{at}mcmaster.ca.

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